Method for producing an electrical contact element



Jan. 29, 1963 H. E. SPOONER 3,075,281

METHOD FOR PRODUCING AN ELECTRICAL CONTACT ELEMENT Filed Oct. 3, 1958FIG. 2 FIGJ mu-mm 1;

IIIIJIIII.

INVENTOR.

HOWARD E. SPOONER BY K642 flaw ATTOR EYS Patented Jan. 29, 19533,075,281 METHOD FUR PRQDUCING AN ELECTRICAL CGNTACT ELEMENT Howard E.Spooner, Lincoln, R.I., assignor, by mesne assignments, to EngelhardIndustries, Inc., Newark, NJL, a corporation of Delaware Filed Oct. 3,1958, Ser. No. 765,234 2 Claims. (Ci. 29-155.55)

This invention relates to a method for producing an electrical contactelement and, more particularly, is con cerned with a method whichpermits the insertion of contact points of precious metal into asupporting base metal strip, the surface of the contact point contactinga base metal. oxide.

It is known that the properties of precious metal contacts are improvedby additions of base metal oxides or mixtures thereof such as iron,cobalt, nickel, copper, cadmium, chromium, manganese, tin and manyothers. The contacts produced from precious metals with added base metaloxides show a decreased tendency to stick during performance and areused in a great number of applications. However, one of the maindifiiculties encountered with this type of contact resides in the factthat the base metal oxide addition renders the material unsolderable andnumerous methods exist to secure such contact points in supports. On theother hand, in US. Patent No. 2,625,737, a method has been described inwhich precious metal contacts are obtained by preparing a disc from alaminated stock sheet metal having a top layer of a precious metal.Subsequently, the disc is inserted into an aperture in a base metalstrip, the aperture having a shape substantially identical with that ofthe disc, the strip serving as the support for the contact. The disc isbonded to the walls of the aperture and finally bent outwardly from theplane of the support, in order to form a raised contact point.

It has been found that this method, as described in US. Patent No.2,625,737, can be successfully employed to produce electrical contactelements having a contacting surface of precious metal admixed with abase metal oxide. This invention therefore constitutes a furtherdevelopment of the method described in the aforementioned US. patent,thereby combining the advantages of precious metal contacts with addedbase metal oxides and those of the known method. Slight modifications ofthe method have been found useful, as described below.

In accordance with the invention, an electrical contact element, havingat least one contact point of a precious metal with an added base metaloxide and being mounted in a supporting base metal strip, is obtained byforming a disc from a laminated metal sheet having two layers, bonded toeach other, the first layer consisting of a precious metal containing ametal oxide whereas the second layer consists of any precious or basemetal capable of being bonded to the desired support by means of a heattreatment, the second layer having a melting point not higher than thatof the first layer. Good results have been obtained when using silver.Subsequently, the disc is inserted into an aperture in the support, ofsubstantially identical shape to that of the disc, whereupon theassembly is subjected to a heat treatment in order to bond the sides ofthe second layer of the disc to the adjacent portions of the walls ofthe aperture. A raised contact point is finally obtained by bending thebonded disc outwardly from the plane of the adjacent portions of thesupport by means of dies and pressure.

In the following, the invention will be described in connection withcontacts of fine silver with added base metal oxide, without beingrestricted thereto, and by reference to the accompanying drawing inwhich one embodiment of the invention is illustrated.

FIGURE 1 is a section through a laminated disc,

FIGURE 2 is a fragmentary section through the supporting base metalstrip,

FIGURE 3 is a fragmentary section through the base metal strip of FIGURE2 having a disc of FIGURE 1 inserted therein,

FIGURE 4 is a section through a finished contact element, and

FIGURE 5 is a section through a punch press suitable for applying themethod of the invention and illustrating the combined steps of formingthe disc and inserting the disc into the supporting strip.

The method of the invention is intended to be used especially inconnection with silver contacts having a base metal oxide added to thecontact surface and therefore will be described in connection therewith,without being limited to silver contacts. Referring to FIGURE 1, a disc8 is provided which consists of a bottom layer 10 of silver having a toplayer 12 of silver thereon with which a selected base metal oxide is inadmixture. For the purpose of mass production, the discs 8 are blankedout from laminated sheet metal stock, as described hereinafter inconnection with FIGURE 5. However, when desired, the top layer may be alayer of silver containing a metal capable of forming an oxide and theoxidation of this metal can be effected at any time during the processand even after the contact element is finished.

FIGURE 2 illustrates the base metal strip 14 forming the support for thecontact and which is fabricated from any desired material such ascopper, brass or the like. At the location where the contact is to beinserted, the strip 14 is provided with an aperture of a shapesubstantially identical with that of the disc, generally in the form ofa circle. Subsequently, the disc 8 is inserted into the aperture asshown in FIGURE 3 and subjected to a heat treatment in a furnace at atemperature within or above the softening range of silver, whereby thewall 16 of the layer 1b of the disc is firmly bonded to the adjacentportion of the wall 18 of the aperture in the support 14. N0 bondingoccurs between the comparatively narrow edge of the layer 12 and theadjacent portion of the aperture wall 18 since this layer contains abase metal or a base metal oxide but it has been found that, for allpractical purposes, when making the layer 10 sufficiently thick, a firmbonding between the disc 8 and the support 14 is obtained. Especiallywhen using silver, the bond is strong enough to permit the final shapingeffected by die pressing and illustrated in FIGURE 4, whereby the disc 8is bent outwardly from the plane of the adjacent portion 2% of thesupport to form a raised contact point.

In the aforementioned U.S. Patent No. 2,625,737, the disc describedtherein has a third layer on its bottom consisting of a solder, which ispartly drawn up around the sides of the disc when the disc is punchedout from the laminated metal stock, and serves to accomplish the bond.Such a solder layer may be used in connection with the present inventionas well, but it has been found that, when the layer 10 is made from ametal having a melting point not higher than that of the first layer,e.g. silver, no solder is required and a sufficiently strong bond isobtained.

Referring to FIGURE 5, a die press suitable for manufacturing contactsin accordance with the invention consists of a die 22 passing through aguide plate 24 and cooperating with a die plate 26 having a bore 23therethrough, the diameter of the bore 28 corresponding to the diameterof the disc 8 punched out by the device. A laminated metal sheetconsisting of a layer 10 of pure silver and a second layer 12 of silvercombined with the In the drawbase metal oxide and bondedto the puresilver layer is passed between the guide plate 24 andthe die- 26.-Sirnultaneously, the base metal strip 14 forming the support is passedthrough a recess 36 in the lower surface of the'die 26 in such a vvaythat the aperture18 is aligned with the bore 28. The punch 22, whenmoving downwardly, punches'out the disc 8 andimmediately' inserts thedisc-into the aperture in'the supporting strip" 14 in one operation. Thestrip 14 carrying one or more discs 8- within one or more apertures issubsequently introduced into a fur'nace andheatedto a temperaturesuitable to insure the bond between the layer 1% of the disc 8- and thewall 13 of'the-ap'ertures in'the'strip 14. Finally, the contact elementsare blanked out-fromthe strip 14 and-shapedby suitable die pressingtothe'forrn shown inFIGURE 4, for example, by bending-over the edges ofthe-strip 14 as shown at 32'and- 34 and by displacing the initial disc 8outwardly frornthe plane of the surrounding portions 211.

It has been pointed out above that-the base metaloxide canbeincorporated intothetop layer 12 f the laminatedstock before blankingout the' discs 8. However, good results have been obtained when using alayer 12made frorn silverand containing ab-ase meta-lcapableofforming anoxide whereby theforrnation oi the oxide in'the layer can be etfeeted atanymoment during the process of manufacturing the contact and: even whenthe contact elerne'ntis finishedi- In'anyevent; astrongbonding of theside wall-16 of the" layer w theadjacent-portions of'the wall 180i theaperture w'ill be-obtained,-which results in a precious metal contactsurface containing a base metal oxide supported by a base metal strip,without the necessity of soldering the oxide-containing material.

It will-be obvious-to those skilled in the'art that many modificationsmay be made within the scope ofthe present inventionwithoutdepartingfrom the spirit thereof; and the invention includes allsuch modifications.

What'is claimed-is:

l. A method for producing an electrical-contact ele-- merit havingatleast one contact point of silver conta'ining a base metaloxideand-mounted'ina base metal support, which comprises forming adisc fromalaminated metal sheet having first and second layersbonded to eachother, the first layer consisting essentially of a thinlayerof silver inadmixture with an oxide of a base metal selected from the groupconsisting of iron, cobalt, nickel, copper, cadmium, chromium,manganese, tin and admixtures thereof, the second layer consistingessentially of a comparatively thicker layer of silver; inserting thedisc into an aperture in said-support; bonding the side wall of thesecond layer of the disc directly tothe adjacent wall of the aperture bymeans, of a heat treatment; and displacing. the bonded disc outwardlyfrom the plane of the-support, to form a raised contact point.

2. A method for producing an electrical contact ele ment havingatleastone contact point of silver containinga base metal oxideandmounted in a base metal support, which comprises forming a disc froma laminatedmetal sheet having first and'second layers bonded toeachother, the first layer consisting essentially of a thin layer of silverin admixture with an oxidizable metal selected'from the group consistingof iron, cobalt, nickel, copper, cadmium, chromium, manganese, tin andadmixturesthereof, the secondv layer consisting. essentially of acomparatively thicker layer of silver; inserting the disc'intoan'aperturein said support; bonding the side wallof the secondlayer ofthe disc directly to the adjacent wall of the aperture by means of aheat treatment; and, displacing the bondeddisc outwardly firomthe planeof'th'e support to form araised-contact point; the method also includingoxidizing-at leasta portion of the oxidizable metal content in thefirstplayer.

References Citedin-the file of this patent UNITEDSTATES PATENTS2,148,040 Schwarzkopf Feb. 21, 1939 2,226,944 Reeve Dec. 31, 19402,360,522 Shobert Oct; 17, 1944 2,365,249 Co'mstock; Dec. 19, l944-2,373,861; Van Inwagen Apr. 17,, 1945 2,382,338 Shobert Aug. 14, 19452,425,052 Swinehart Aug. 5', 1947 25,425,053- Swinehart Aug. 5, 19472,625,737 Spooner Jan. 20, 1953 2,861,155 Farnham Nov. 18, 1958

1. A METHOD FOR PRODUCING AN ELECTRICAL CONTACT ELEMENT HAVING AT LEASTONE CONTACT POINT OF SILVER CONTAINING A BASE METAL OXIDE AND MOUNTED INA BASE METAL SUPPORT, WHICH COMPRISES FORMING A DISC FROM A LIMINATEDMETAL SHEET HAVING FIRST AND SECOND LAYERS BONDED TO EACH OTHER, THEFIRST LAYER CONSISTING ESSENTIALLY OF A THIN LAYER OF SILVER INADMIXTURE WITH AN OXIDE OF A BASE METAL SELECTED FROM THE GROUPCONSISTING OF IRON, COBALT, NICKLE, COPPER, CADMIUM, CHROMIUM,MANGANESE, TIN AND ADMIXTURES THEREOF, THE SECOND LAYER CONSISTINGESSENTIALLY OF A COMPARATIVELY THICKER LAYER OF SILVER; INSERTING THEDISC INTO AN APERTURE IN SAID SUPPORT; BONDING THE SIDE WALL OFF THESECOND LAYER OF THE DISC DIRECTLY TO THE ADJACENT WALL OT HE APERTURE BYMEANS OF A HEAT TREATMENT; AND DISPLACING THE BONDED DISC OUTWARDLY FROMTHE PLANE OF THE SUPPORT TO FORM A RAISED CONTACT POINT.